The conventional technology applies interference effects in thin films to adjust the intensity and phase for different wavelengths, angles of incidence, and polarization states to meet the demands of various optical components, such as anti-reflection coatings, high-reflection coatings, beam splitters and band-pass filters. However, the components are limited by the fact that the polarization states of incident light and reflected light are the same. The present invention proposes a method that uses an anisotropic thin film system to generate strong polarization conversion. Polarization conversion from an anisotropic thin film was only discussed by Ian Hodgkingson et al. on the computational results of the air/anisotropic thin film/substrate system, but the reflectance was too small (less than 10−3), thus could be hardly measured and applied. Therefore, using thin film interference on polarization conversion and application was not proposed otherwise.
F. Yang and J. R. Sambles suggested using the boundary of an anisotropic optical medium to have polarization conversion reflectance, but it achieved low intensity of polarization conversion. Using anisotropic thin film here not only could enhance the polarization conversion ratio but also could design and fabricate multilayered system to have polarization conversion for specific wavelength range or incident angle range.
In measurement, the measurement of anisotropic optical constants (including the index of refraction, orientations of principal axes, and thickness) usually uses an ellipsometer as the main method. However, since ellipsometers are based on both intensity and phase measurements, its cost is very high. The optical-constants of the anisotropic film can be determined to have the anisotropic thin film in the module proposed in the present invention and measure polarization conversion reflectance versus angle of incidence and wavelength. This technology could enhance the detection sensitivity significantly, and save cost because it only measures intensity.